Williston – Toys R Us was evacuated for about two hours Tuesday due to elevated carbon monoxide levels.

Williston and Essex Junction fire responded at 10:22 a.m. to a call about a suspicious odor in Toys R Us, located at 244 Retail Way, according to officials.

Williston firefighters evacuated approximately 75 people from the store and then found carbon monoxide levels of 120 parts per million, said Fire Chief Ken Morton.

“It’s a pretty high level,” Morton said. Vermont Gas Systems also responded to the store briefly in case the odor had been related to a gas problem, he said.

Carbon monoxide is an odorless gas. The National Institute for Occupational Safety and Health has set a carbon monoxide exposure ceiling at 200 parts per million, according to the U.S. Environmental Protection Agency’s website.

St. Michael’s Rescue and Essex Rescue transported two people to Fletcher Allen Health Care because they were “not feeling well,” Morton said. No additional details on their condition were available.

Firefighters ventilated the building with fans and used ladder trucks to reach the store’s rooftop units. Morton said the source of the gas was a propane-powered floor treatment unit that had been used the night before. Morton said Thursday afternoon that the store would not use the unit again until it could be tuned and tested.

Customer Damon Henderson of St. Johnsbury was about to check out at Toys R Us when firefighters entered the store and began the evacuation, he said. He and his wife and daughter had to leave their purchases in bags at the door because the cashier had not yet processed their check.

Henderson said he had noticed a propane smell when he entered the store. The family waited in the Toys R Us parking lot to be allowed to pick up their purchases — the last of their Christmas shopping, Henderson said.